Mobile fluid distribution system and method

ABSTRACT

A fluid distribution system and method for mobile applications. The system includes a power source, a pump driven by the power source, and a motor driven by the pump. The system also includes a spray head with a fluid inlet passage, a fluid outlet passage, a fluid piston disposed in a chamber for controlled access between the inlet and outlet passages and defining a variable orifice, and a hydraulic cylinder controllably engaged to the orifice. The fluid piston and the hydraulic cylinder are aligned with a common longitudinal axis, and the inlet passage is offset from the axis in a direction opposed to the location of the outlet passage.

TECHNICAL FIELD

This disclosure relates generally to a system and method for fluiddistribution and, more particularly, to a system and method forcontrolled distribution of a fluid in a mobile environment.

BACKGROUND

Fluid distribution systems, in particular mobile fluid distributionsystems, are used in a variety of applications. For example, at miningand construction sites, it is common to use mobile fluid distributionsystems to spray water over routes and work areas to minimize thecreation of dust during operations. A specific example might include awater truck that sprays water over roads at a mine site.

Other applications of mobile fluid distribution systems may includespraying of pesticides and herbicides, e.g., for agricultural use,disbursement of saline solutions on roads for snow and ice control, firesuppression, and the like.

For various reasons, such as cost and consistent fluid application, itis desired to maintain control of the amount and pattern of fluids beingdistributed, in particular with regard to maintaining a uniform andconsistent application of fluid per unit of area. For example, whenspraying water on mine roads, it may be desired to uniformly distributethe water over the road surface to avoid applying excess water inspecific locations.

Typical fluid distribution systems spray fluids at pressures that aredirectly proportional to engine speeds of the mobile machines. Operatorsattempt to keep fluid pressure, and the resultant flow of fluids,relatively constant by maintaining constant engine speeds, at least tothe extent possible. These efforts typically require operating mobilemachines at reduced transmission gear ratios to maintain desired enginespeeds. However, these efforts cannot be maintained, for example, whenascending or descending steep inclines, conditions which generallyrequire changing engine speeds.

Efforts have been made to maintain fluid pressures in proportion tomachine speed, i.e., ground speed, rather than engine speed. Althoughthis has resulted in improved fluid distribution per unit area, it isstill difficult to maintain precise control during various operatingmaneuvers, such as starting and stopping, and as operating conditionsvary. Furthermore, many of these systems still distribute fluids inproportion to fluid pressure, which adds to the difficulty of consistentapplication per unit of area.

One example of an attempt to achieve uniform fluid application isdescribed in U.S. Pat. No. 5,964,410 to Brown et al. (the Brown patent).Brown employs spray heads with variable orifices to attempt maintenanceof constant velocities and exit flow trajectories. The spray heads arepressure controlled, however, relying on pressure of the fluid beingsprayed to overcome a spring force to open the spray nozzle.Furthermore, the components that are used to control the nozzle arelocated in the main fluid flow chamber, and thus are susceptible tocorrosion and contamination by particles and debris in the fluid. As aresult, the system would still have difficulty achieving consistentapplication of the fluid per unit of area during various operatingconditions.

The present disclosure is directed to overcoming one or more of theproblems as set forth above.

SUMMARY

In one aspect of the present disclosure a fluid distribution system isdisclosed. The system includes a power source, a pump driven by thepower source, and a motor driven by the pump. The system also includes aspray head with a fluid inlet passage, a fluid outlet passage, a fluidpiston disposed in a chamber for controlled access between the inlet andoutlet passages and defining a variable orifice, and a hydrauliccylinder controllably engaged to the orifice. The fluid piston and thehydraulic cylinder are aligned with a common longitudinal axis, and theinlet passage is offset from the axis in a direction opposed to thelocation of the outlet passage.

In another aspect of the present disclosure a method for distributing afluid is disclosed. The method includes determining a ground speed of amobile machine, determining a pressure of fluid being delivered to aspray head having a variable orifice, comparing the determined pressureto a desired fluid pressure, controlling a motor to maintain the desiredfluid pressure, and controlling the variable orifice as a function ofthe ground speed and independent of fluid pressure to maintain a desireddistribution of fluid.

In yet another aspect of the present disclosure a spray head for a fluiddistribution system is disclosed. The spray head includes a fluid inletpassage, a fluid outlet passage, a fluid piston disposed in a chamberfor controlled access between the inlet and outlet passages and defininga variable orifice, and a hydraulic cylinder controllably engaged to theorifice. The fluid piston and the hydraulic cylinder are aligned with acommon longitudinal axis, and the inlet passage is offset from the axisin a direction opposed to the location of the outlet passage.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagrammatic illustration of a mobile machine suited for usewith the present disclosure;

FIGS. 2A and 2B are diagrammatic views of a spray head suited for usewith the present disclosure;

FIG. 3 is a cut-away view of the spray head of FIGS. 2A and 2B;

FIG. 4 is a representative block diagram of a fluid distribution system;

FIGS. 5A and 5B are representative diagrams of a hydraulic system suitedfor use with the fluid distribution system of FIG. 4;

FIG. 6 is a flow diagram depicting a method of the present disclosure;

FIG. 7 is a flow diagram depicting another method of the presentdisclosure; and

FIG. 8 is a diagrammatic representation of an operator control suitedfor use with the present disclosure.

DETAILED DESCRIPTION

Referring to the drawings, a mobile fluid distribution system 100 andmethod for distributing fluids is shown.

Referring to FIG. 1 in particular, a mobile machine 102 suited for usefor distributing fluids is depicted. The mobile machine 102 of FIG. 1 isshown as a truck, i.e., typical for use in off-highway applications,converted for use to distribute fluids. However, other types of mobilemachines may be employed, for example, articulated trucks, on-highwaytrucks, tractor-scrapers, tractors in combination with trailers, and thelike.

Although not labeled as such in FIG. 1, the mobile machine 102 is fittedwith a fluid tank (element 430 in FIG. 4), and is shown with a varietyof piping, hoses, pumps and valves for fluid distribution purposes. Inparticular, the mobile machine 102 in FIG. 1 is shown as an off-highwaytruck configured as a water truck for spraying water at a work site thattypically generates much dust during work operations. The presentdisclosure, however, may also apply to other types of mobile machinesset up to distribute water or other types of fluids in a wide variety ofapplications. For example, a tractor pulling a trailer may be used todistribute chemicals in agricultural settings, an on-highway truck maybe configured to spray a saline solution on roads, runways, or parkinglots to melt snow and ice, and other varieties of applications andsetups may be used.

FIGS. 2A and 2B illustrate views of a spray head 200 that may be usedwith the present disclosure. As shown more clearly and in more detail inFIG. 3, the spray head 200 may be assembled in relation to alongitudinal axis 312 for reference purposes. For example, the sprayhead 200 includes a fluid inlet passage 302 and a fluid outlet passage304. The outlet passage 304 may be located at a position offset from thelongitudinal axis 312. The inlet passage 302 may be located at aposition offset from the longitudinal axis 312 and in a directionopposed to the location of the outlet passage 304. The location of theinlet passage 302 relative to the location of the outlet passage 304,i.e., on opposite sides of the longitudinal axis 312, may contribute toproviding a laminar flow of fluid from the spray head 200. Such laminarflow may result in a flat spray pattern having droplets of a minimalsize large enough to achieve reduced atomization of the fluid. In awater truck example, this may contribute to optimal fluid control fromthe spray head 200 to a desired surface during mobile spraying.

A fluid piston 306 disposed in a chamber 307 of the spray head 200defines a variable orifice 308 and may provide controlled access betweenthe inlet passage 302 and the outlet passage 304. Controllably engagedto the orifice 308 is a hydraulic cylinder 310. More specifically, thehydraulic cylinder 310 includes a hydraulic piston 316 connected to arod 322, which in turn is connected to the fluid piston 306. Inoperation, as the hydraulic piston 316 is controlled to move, i.e.,linear with the longitudinal axis 312, the rod 322 moves and the fluidpiston 306 subsequently moves, which results in a change in size of theorifice 308.

In the embodiment shown in FIG. 3, the hydraulic cylinder 310 is adouble acting hydraulic cylinder 310. That is, the hydraulic cylinder310 is hydraulically controlled to move in either direction. In moredetail, the hydraulic piston 316 includes a head end 318 and a rod end320. The hydraulic cylinder 310 includes a first hydraulic port 324positioned to allow hydraulic fluid in the hydraulic cylinder 310 at therod end 320, and a second hydraulic port 326 positioned to allowhydraulic fluid in the hydraulic cylinder 310 at the head end 318.Detailed operation of hydraulic circuits that may be used to control thespray heads 200 is described below.

The hydraulic cylinder 310 may include a spring 328 disposed in the headend 318. The spring 328 may provide additional force to hold the orifice308 in a closed position, for example when the hydraulic circuits areshut down. The spring 328 may also be used to supplement the forceapplied to the head end 318 of the hydraulic cylinder 310. For example,the spring 328 may be selected having a desired compression rate (e.g.,force per unit of compression). The total forces applied to the head end318 may be from a combination of hydraulic fluid supplied to the secondhydraulic port 326 and the force of the spring 328, and the total forcesapplied to the rod end 320 may be from a combination of hydraulic fluidsupplied to the first hydraulic port 324 and pressure from fluidentering the inlet passage 302. If the fluid pressure entering the inletpassage 302 is kept fairly constant, then control of the degree ofopening of the orifice 308 may be attained by varying the hydraulicfluid to the first hydraulic port 324.

It is noted that the spray head 200 may be configured for control of thefluid piston 306 by use of other configurations. For example, thehydraulic cylinder 310 may be configured without the second hydraulicport 326 and the associated hydraulic components, thus relying onhydraulic pressure on the rod end 320 and spring pressure on the headend 318.

It is further noted that the spray head 200 may be configured forcontrol by other than a hydraulic piston 316. For example, the hydrauliccylinder 310, hydraulic piston, 316, and all associated hydrauliccircuits and components could be replaced by electrical or mechanicalactuators. As specific examples, the fluid piston 306 may be controlledby an electrical actuator such as a solenoid (not shown), or may becontrolled by a mechanical actuator which may include any of a varietyof cams, screws, levers, fulcrums, and the like (also not shown).

The hydraulic cylinder 310 may be fluidically isolated from the chamber307, thus isolating the fluid that passes through the orifice 308 fromthe hydraulic fluid in the hydraulic cylinder 310. This design offersthe advantage of keeping particles and contaminants away from thecomponents in the hydraulic cylinder 310, for example when water fromretaining ponds is used for dust suppression applications.

The spray head 200 may include one or more fluid deflectors 314connected to the spray head 200 and configured to control a fluiddistribution pattern from the outlet passage 304. For example, two fluiddeflectors 314 are shown in FIG. 3 (and may be viewed in FIGS. 2A and2B, although not labeled as such). The fluid deflectors 314 may beconfigured to control the fluid distribution pattern, for example in alaminar flow, from the outlet passage 304 in furtherance of the laminarflow control that may be provided by the above-described specificlocations of the inlet and outlet passages 302,304 relative to thelongitudinal axis 312.

A seal plate 330, attached to the fluid piston 306, may be used tofurther deflect fluid to attain a desired spray pattern, for example bydesigning the seal plate 330 with a desired shape and physicalconfiguration.

Referring to FIG. 4, a block diagram of a representative portion of afluid distribution system 100 is shown. For exemplary purposes, FIG. 4is described as applied to a mobile machine 102, i.e., an off-highwaytruck, set up for use as a water truck at a mining or construction site,although the fluid distribution system 100 shown in FIG. 4 could be usedin other applications as noted above.

A power source 402 to supply power for the fluid distribution system 100may also be used to supply motive power for the mobile machine 102. Forexample, the power source 402 may include a prime mover 404 for themobile machine 102. The prime mover 404 may include an engine 406drivingly connected to the mobile machine 102 and a transmission 408driven by the engine 406. The engine 406 and transmission 408 may bechosen from among many types and configurations that are well known inthe art. It is also well known to use the power supplied by prime movers404 for other purposes in addition to providing motive power. Forexample, an off-highway truck, prior to being configured for waterdistribution applications, may have been designed to use power from theprime mover 404 for applications such as raising and lowering a truckbed.

A pump 410, driven by the power source 402, is in turn configured todrive a motor 412. The pump 410 may be driven by the engine 406 or thetransmission 408 by means that are known in the art, and may be ahydraulic pump 410 as is also known in the art. The pump 410 may beconfigured to drive the motor 412 by well known hydraulic means. Ahydraulic tank 428 may be used to supply and recover hydraulic fluid toand from the pump 410 and motor 412.

In the embodiment shown in FIG. 4, the pump 410 may be a fixeddisplacement type and the motor 412 may be variable displacement. Forexample, an off-highway truck configured for use as a water truck mayhave an existing fixed displacement pump 410 already in place for otherpurposes. Adding a variable displacement motor 412 may offer advantagesin control of the fluid distribution system 100, for example by enablingcontrol of fluid pressure to maintain the fluid at a constant desiredpressure regardless of engine speed or ground speed. A fixeddisplacement pump 410 may still be used for applications other thanfluid distribution without being affected by changes in fluiddistribution parameters. For example, the pump 410 may drive the motor412 and also drive a system for cooling brake components (not shown).The brake cooling system would not be affected by load changes from thefluid distribution system 100. In alternative embodiments, the pump 410and motor 412 may be other combinations of fixed and variabledisplacement devices, for example a variable displacement pump and afixed displacement motor.

The motor 412 is fluidly connected to one or more spray heads 200, e.g.,three spray heads as shown in FIG. 4. More specifically, the motor 412may provide hydraulic power to a fluid pump 426, which in turn deliversfluid by way of fluid lines 432 to the inlet passages 302 and throughthe orifices 308 of the spray heads 200. The fluid pump may obtain fluidfrom a fluid tank 430, for example a water tank mounted on a watertruck.

Although the three spray heads 200 in FIG. 4 are shown connected bycommon fluid lines 432 to the fluid pump 426, each spray head 200 may beindependently controllable. In addition, each spray head 200 may includean orifice 308 that is continuously variable from a fully closedposition to a fully open position, as distinguished from an orifice thatis capable of only being open or closed.

A ground speed sensor 414, located on the mobile machine 102, may beconfigured to sense a ground speed as the machine moves. The groundspeed sensor 414 may be located to sense ground speed based on operationof the transmission 408, rotational movement of a ground engaging member(not shown) such as a wheel, or by some other method known in the art.

A fluid pressure sensor 416 may be located to sense pressure of fluid influid lines 432, or alternatively fluid pressure exiting fluid pump 426.

An engine speed sensor 418 may be located to sense the speed of theengine 406.

A transmission state sensor 420 may be located to sense the state, e.g.,forward, neutral, or reverse, of the transmission 408. The transmissionstate sensor 420 may alternatively sense direction of motion of themobile machine 102 to determine transmission state.

Any of the above sensors may be configured to directly sense a desiredparameter, may sense one or more secondary parameters and derive a valuefor the desired parameter, or may determine a value for the desiredparameter by some other indirect means. Operation of the above sensorsfor their intended purposes are well known in the art and will not bedescribed further.

A controller 422 may receive sensed or derived signals from the groundspeed sensor 414, the fluid pressure sensor 416, the engine speed sensor418, and the transmission state sensor 420. The controller 422 may alsobe controllably connected to one or more of the motor 412 and the sprayheads 200. For example, and as described in more detail below, thecontroller 422 may use information received from the ground speed sensor414 and the fluid pressure sensor 416 to determine a desired fluidpressure to maintain, and responsively control the variable displacementof the motor 412 to maintain a constant fluid pressure. The controller422 may also use information received from the engine speed sensor 418for further control of the variable displacement motor 412. Thecontroller 422 may also use the above received information to controlthe variable orifices 308 of the spray heads 200 to control a flow rateof the fluid being delivered to and sprayed from the spray heads 200. Inone specific example, the controller 422 may determine from thetransmission state sensor 420 if the mobile machine 102 is moving inreverse, and responsively shut off the fluid distribution system 100during this condition.

An operator control device 424, located in a cab compartment (not shown)of the mobile machine 102, may provide an operator with a variety ofcontrol and display functions for the fluid distribution system 100. Theoperator control 424 may be of any desired configuration and may becustom designed for specific mobile machines and applications.

Referring to FIG. 8, the operator control 424 may include a display 802.The display 802 may be used to provide visual indication of a widevariety of information including, but not limited to, a currentoperating mode of the fluid distribution system 100, various sensed anddetermined parameters (such as engine and ground speeds, fluidpressures, and the like) fluid levels in the fluid tank 430, and anyother information desired to be provided. The display 802 may includevisual display of information and may also include audible alerts suchas low levels of fluid in the fluid tank 430, and the like.

Various operating modes may be selected from the operator control 424through the use of a wide variety of operator input devices (not shown)which may include, but are not limited to, switches, dials, levers,joysticks, buttons, and the like. FIG. 8 lists a sampling of availablemodes in no particular order. The list is not meant to be all-inclusiveand additional modes may be made available as desired.

Pre-programmed spray modes may allow an operator to select from among avariety of spray modes based on the intended application. It may also bea feature that additional modes may be programmed for later use.

Manual mode may allow an operator to set up desired parameters, forexample selecting a desired pressure, flow rate, number of active sprayheads, spray pattern, and the like.

Intermittent mode may allow an operator to select a pulsing spraypattern that may be adjusted as a function of time or spray distance.

Fire fighting mode may allow the fluid to be diverted to a spray cannon(not shown), hose reel (not shown), and/or to any combination of sprayheads 200.

Tank fill mode may enable pumps and valves needed to pump fluid into thefluid tank 430. Tank fill mode may be set up to be automatic,semi-automatic, or manual. Alternatively to pumping fluid into the fluidtank 430, tank fill mode may provide for filling of the fluid tank 430by gravity or external pumping means.

Cleanout mode may be used to open each orifice 308 to a maximum openposition to flush debris from the spray heads 200. This feature may beparticularly useful, for example, when a water truck obtains water froma pond or stream, thus introducing sediment, debris and particles intothe fluid tank 430.

Oncoming traffic cutout mode may be used to quickly and easily shut offspecific spray heads 200 that otherwise would undesirably direct sprayonto objects, such as other vehicles passing the mobile machine 102.This feature may be needed for a short duration only, and thus may becontrolled by use of a momentary contact switch or trigger.

Referring to FIGS. 5A and 5B, various embodiments of a hydraulic system500 suited to control a portion of the fluid distribution system 100 isshown. The hydraulic system 500 is representative only and is not meantto be limiting in scope and application. For illustrative purposes only,four spray heads 200 are shown.

Each hydraulic cylinder 310 may be double acting, i.e., each hydraulicpiston 316 is controlled at both a head end 318 and a rod end 320. Ahead end valve 502, hydraulically connected to the second hydraulic port326, is controlled to apply pressure to the head end 318, thus drivingthe orifice 308 toward a closed position. A rod end valve 504,hydraulically connected to the first hydraulic port 324, is controlledto apply pressure to the rod end 320, thus driving the orifice 308toward an open position.

FIG. 5A depicts one head end valve 502 controlling all spray heads 200simultaneously, and one rod end valve 504 controlling each spray head200 individually. In this configuration, the single head end valve 502applies pressure to all spray heads 200 toward a closed position, andeach rod end valve 504 is independently controlled to apply pressure toa corresponding spray head 200 toward an open position. Otherconfigurations may be used, however, without deviating from the scope ofthe present disclosure. For example, as depicted in FIG. 5B, multiplehead end valves 502 may be used to control a corresponding number ofspray heads 200 individually.

A hydraulic supply 506 and a hydraulic tank 508 supply hydraulic fluidto and from the head end and rod end valves 502,504. Although thehydraulic supply 506 and hydraulic tank 508 are shown as separate unitsfor each valve (for ease of illustration), it is contemplated that onehydraulic supply 506 provides pressurized hydraulic fluid to all of thevalves 502,504, and one hydraulic tank 508 provides a return to tankpath for all of the valves 502,504. The hydraulic supply 506 may be adedicated supply, e.g., a pilot supply, located on the mobile machine102, or may be part of a larger hydraulic system which may include thepump 410. In like manner, the hydraulic tank 508 may be a separate tankor may be associated with the hydraulic tank 428.

INDUSTRIAL APPLICABILITY

An example of application of the present disclosure can be describedwith reference to the flow diagrams of FIGS. 6 and 7.

Referring to FIG. 6, in a first control block 602, a ground speed of themobile machine 102 is determined. The ground speed may be senseddirectly, for example by a ground speed sensor 414, or may be determinedby other means known in the art.

In a second control block 604, a fluid pressure of the fluid lines 432is determined. The fluid pressure may be sensed directly, for example bya fluid pressure sensor 416, or may be determined by other means knownin the art. The fluid pressure may be determined from the fluid lines432 directly, or may be determined at some other location associatedwith the fluid lines 432, such as the spray head 200, the fluid pump426, the pump 410, the motor 412, or some other location. The fluidpressure may also be determined at multiple locations.

In a third control block 606, the determined fluid pressure is comparedto a desired fluid pressure. The desired fluid pressure may be set basedon a pre-programmed spray mode, a manually input desired fluid pressure,by some other operating mode of the fluid distribution system 100, or bysome other determined or input parameter.

In a fourth control block 608, the motor 412 is controlled to maintainthe determined fluid pressure at the desired fluid pressure. The motor412 may be a variable displacement motor 412, which may be controlled byvarying the displacement of the motor 412, as is well known in the art.Alternatively, the pump 410 may be a variable displacement pump 410 thatmay be controlled for the same purpose. Other types of controllablepumps and motors, such as electric and such, may also be used to controlthe fluid pressure. As an alternative to controllable pumps and/ormotors, other means known in the art, such as variable orifices, valves,and the like, may be used to maintain the fluid pressure as well.

In a fifth control block 610, each variable orifice 308 is controlled tomaintain a desired distribution of fluid. In a fluid distribution system100 having multiple spray heads 200, and thus a corresponding multipleof orifices 308, each variable orifice 308 may be controlled independentof each other variable orifice 308, and all orifices 308 may becontrolled independent of fluid pressure. The variable orifices 308 maybe controlled to maintain a desired fluid distribution, for example adesired fluid distribution per unit of area. Control of the variableorifices 308 may be accomplished by controllably opening and closingeach orifice in a manner described above with reference to FIG. 3.Opening and closing an orifice 308 is a variable process, thus providinga continuously variable number of orifice positions for optimal controlof the distribution of fluid.

Referring to FIG. 7, a flow chart depicting another method of thepresent disclosure is shown.

In a first control block 702, a condition associated with a location forfluid distribution is determined. Although a number of conditions may bedetermined, for illustrative purposes an exemplary condition of a levelof dryness associated with the location is described. The level ofdryness may be determined, for example in a water truck application, byan operator's observations of a relative dryness of the roads andsurfaces to be sprayed. Alternatively, other more automated means fordetermining a level of dryness may be used.

In a second control block 704, a desired fluid pressure as a function ofthe determined condition is determined. The desired fluid pressure maybe a modification of the desired fluid pressure associated with themethod described with reference to FIG. 6.

In a third control block 706, the motor 412 is controlled to maintainthe desired fluid pressure, in the same manner as described above withreference to FIG. 6.

In a fourth control block 708, the variable orifice 308 is controlled asa function of both the ground speed and the determined condition tomaintain the desired distribution of fluid.

The present disclosure provides a mobile fluid distribution system 100and method which offers many advantages, among which includes providingcontrol of fluid distribution over a desired area, in particular controlof an amount of fluid distributed over a desired unit of area undervarying conditions. Maintaining a constant fluid pressure while varyingthe flow rate through individual spray heads 200 provides more precisecontrol of fluid distribution and the capability for a number ofspecialized flow control modes.

Other aspects can be obtained from a study of the drawings, thespecification, and the appended claims.

1-8. (canceled)
 9. A method for distributing a fluid, the methodcomprising the steps of: determining a ground speed of a mobile machineconfigured for fluid distribution; determining a pressure of fluid beingdelivered to a spray head having a variable orifice; comparing thedetermined pressure to a desired fluid pressure; controlling a variabledisplacement motor to maintain the desired fluid pressure based on thecomparison; and controlling a size of the variable orifice duringoperation as a function of the ground speed and independent of fluidpressure to vary a flow rate of fluid output from the spray head tomaintain a desired distribution of fluid.
 10. (canceled)
 11. A method,as set forth in claim 9, wherein controlling the size of the variableorifice includes the step of controlling sizes of a plurality oforifices on a corresponding plurality of spray heads.
 12. A method, asset forth in claim 11, wherein controlling sizes of a plurality oforifices includes the step of controlling the sizes of the plurality oforifices independent of each other.
 13. A method, as set forth in claim9, further including the steps of: determining a condition associatedwith a location for fluid distribution; determining a desired fluidpressure as a function of the condition; controlling the variabledisplacement motor to maintain the desired fluid pressure; andcontrolling the variable orifice as a function of the ground speed andas a further function of the determined condition to maintain thedesired distribution of fluid.
 14. A method, as set forth in claim 13,wherein determining a condition includes the step of determining a levelof dryness associated with the location. 15-20. (canceled)
 21. A method,as set forth in claim 9, further including the step of controlling apump to adjust a pressure of fluid being delivered to the spray head.22. A method, as set forth in claim 9, wherein controlling a size of thevariable orifice includes the step of controlling movement of a fluidpiston of the spray head.
 23. A method, as set forth in claim 9, furtherincluding the step of controlling a fluid distribution pattern.
 24. Amethod, as set forth in claim 23, wherein the fluid distribution patternis laminar flow.
 25. A method, as set forth in claim 9, wherein thedesired distribution of fluid is a desired distribution per unit ofarea.
 26. A method, as set forth in claim 11, wherein controlling sizesof the plurality of orifices includes the step of controlling movementof a fluid piston of each of the corresponding plurality of spray heads.27. A method, as set forth in claim 11, further including the step ofcontrolling a fluid distribution pattern.
 28. A method, as set forth inclaim 27, wherein the fluid distribution pattern is laminar flow.
 29. Amethod, as set forth in claim 11, wherein the desired distribution offluid is a desired distribution per unit of area.
 30. A method, as setforth in claim 9, wherein an operator may select a spray mode.
 31. Amethod, as set forth in claim 9, wherein determining a pressure of fluidbeing delivered to a pray head includes the step of determining apressure of fluid at multiple locations.
 32. A method, as set forth inclaim 9, wherein the operation includes fluid distribution.
 33. Amethod, as set forth in claim 11, wherein the operation includes fluiddistribution.
 34. A method, as set forth in claim 9, wherein thevariable orifice is continuously variable.
 35. A method, as set forth inclaim 11, wherein the plurality of orifices are continuously variable.